Vaccine with mRNA is preferred: new recommendations

Canada's National Advisory Committee on Immunization (NACI) has updated guidelines on the use of COVID-19 vaccines. The committee now considers that those who have had their first vaccination with AstraZeneca vaccine are preferred to receive mRNA vaccines: Pfizer or Moderna as a second dose. The change was announced by Canada's Chief Medical Officer of Health, Dr. Teresa Tam.

According to Tam, evidence suggests that people develop a "better immune response" when the first dose of AstraZeneca is followed by a second dose of Pfizer or Moderna. The doctor stressed, however, that people in Canada who have received both doses of AstraZeneca should also be reassured that the vaccine provides good protection against the virus, as well as against severe disease and hospitalization.

In the new guidance, NACI also recommended using mRNA vaccines as the first dose unless contraindicated. In addition, the clause stating that mRNA vaccines are interchangeable has been eliminated. According to the new guidelines, the second vaccination must be given with the same mRNA vaccine with which the first vaccine was given. Only situations where a product is not available are considered exceptions.

The document has caused public confusion and NACI has been criticised for constantly changing recommendations. This is mainly because less than two weeks ago, NACI allowed vaccinations with different vaccines and talked about how Pfizer and Moderna are interchangeable and perfectly safe. The provinces of Ontario and Quebec announced the ability to vaccinate with different drugs just hours before the new guidance was published.

"One of the things I will remember most from the pandemic is how many times NACI publicly made high-profile statements, scaring and outraging the public, and the pharmacists and doctors who give vaccinations suffered," shared Dr. Kelly Grindrod, assistant professor of pharmacy at the University of Waterloo.

But some health experts believe that NACI has taken the right step by updating the vaccine guidelines. They particularly supported the recommendation to obtain an mRNA vaccine after the first dose of AstraZeneca, which is important against the background of the spread of the Delta variant, also known as the Indian strain, against which AstraZeneca has proved less effective.